Earth’s self-regulation is weaker than assumed

The MPI-M team used three Reanalysis data sets from 1993 to 2023, which use weather  models and observations to provide a consistent description of atmospheric conditions over long periods of time. The team considered temperature and humidity variations in the reanalyses and calculated the related changes in the radiant energy transport. The results differ depending on whether seasonal or inter-annual variability is considered—especially before 2008. After that, there is much better agreement between these two values, as well as among the three data sets, which the scientists attribute to improved satellite-based instruments incorporated by each of the reanalysis products.

The MPI-M team finds that the calculated average value for the clear-sky long-wave feedback parameter is 10 to 20 percent lower than predicted for an atmosphere with a fixed relative humidity. “This means that the Earth reacts more sensitively to radiative forcing than previously thought,” says Gloeckner.

The researchers further show that inter-annual variability associated with El Niño-Southern Oscillation imposes a positive correlation between warming and drying. Without such a correlation, i.e. in the case of constant relative humidity, their estimate of the feedback would have been even weaker. According to the scientists, it is necessary to continue observing the long-term variability of humidity in the atmosphere and to clarify why observations and theory lead to different calculated feedback strengths.